It seems to be implied that if a team uses priorities at all, then they need to prioritize all the books in the project scope. This need not be the case. The reality is that you can use priorities for special projects like The Life of Abraham, The Joseph story, or the Christmas story, and once you are back to only working on complete books then simply use the Assignments and Progress window to assign books as needed. Priorities give the most value when you want to create custom units of chapters to work on. They do not add much if you are working on complete books. Having said that, if you feel that making units for lets say, the Synoptics, or the Pauline epistles would help your team, then Priorities of groups of books can be helpful. The fact that if I define Synoptics as a priority, then I can filter and do assignments for all three synoptic Gospels easily. Others may have other opinions about how useful priorities are for teams only doing complete books.